The main condition of efficiency of ion generators is a high ratio of the number of ions leaving the generator to the total number of ions generated by this generator. Realization of this condition largely depends on the ion emitter structure and its position in the generator.
There are such known ion emitters made of a plurality of needles, for example, those described in U.S. Pat. Nos. 4,433,123; 4,498,116; 4,689,715; 4,757,422, 5,837,035 and 6,850,403.
While the advantage of such emitters is their directed ionization from the needle tips, a significant drawback is related to the difficulty to make needles with tips of equal sharpness, which results in uneven ionization when a number of needles are used.
Ion emitters are also known in which the needles are shaped as a planar structure made from conducting material. This structure is positioned on one side of the insulating base at a considerable distance from its edge, while another planar structure used as a second electrode is positioned at the other side thereof. Such devices are described in U.S. Pat. Nos. 7,254,006 and 7,256,979 and in WO 2004/102755, JP 2004103257(A) and JP 2006066229.
A significant drawback of these emitters is the use of a large number of needles, which occupy a great deal of space. This is due to the fact that the corona discharge is generated within the insulating base between the elements of the single cells of the planar structure.
The external ion flow of each element is extremely small; hence a large number of cells is needed to achieve the required output level.
Also known are ion emitters made from a thin wire with emission occurring along the entire length thereof Such devices are described in U.S. Pat. Nos. 4,516,991 and 6,635,106.These emitters are advantageous in that the metal emitters do not cause notable change of the geometric size owing to the long and thin design of the emitter.
Nevertheless, a significant disadvantage of such emitters is that the ion emission occurs at right angles to the wire axis in all directions, which impairs the efficiency of ion generation.
Another important objective related to the ion generators is removing of dust settled on the emitter during the use. Dust settled on the emitter impairs the ion emission level because of the isolation of the ionizing (sharp) part of the emitter. In particular, when the emitter is in the form of an array of closely packed needles, dust is trapped between the needles and is difficult to remove.
There are known methods of removing of dust settled on needle emitters and apparatus thereof, for example those described in U.S. Pat. Nos. 4,734,580 and 5,153,811.
In the above-mentioned devices a cleaning device for removing dust is provided comprising brushes located between the needles and the screen. A significant disadvantage of known device is the large depth of the cleaning device, owing to which the needles must be placed at a considerable distance from the screen, which reduces the efficiency of the ion generator.